HMO Export in Engineered Microbial Hosts for Fermentation Purity
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Solution Overview
Problem
Current methods for producing complex human milk oligosaccharides (HMOs) face challenges in large-scale production due to inefficient export of these molecules from bacterial cells during fermentation, leading to unwanted precursor mixtures in the fermentation medium, and there is a lack of effective transport systems for larger oligosaccharides.
Innovation Solution
Genetically modify microbial host cells to overexpress specific glycosyltransferases and modify sugar export proteins, such as YjhB or SetA, to enhance the export of desired oligosaccharides like lacto-N-triose II into the culture medium, while inhibiting the export of precursors, using secondary active transporters and optimizing metabolic pathways for precursor import.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional fermentation processes are used to produce complex HMOs, then production can proceed with standard microbial hosts, but the export of oligosaccharides from bacterial cells is inefficient, leading to unwanted precursor mixtures in the fermentation medium
Solution Approach 1:
The patent introduces specific exporter proteins (such as SetA, YjhB, or engineered MFS transporters) as intermediary components that mediate the selective transport of complex HMOs from the bacterial cell interior to the external medium. These exporter proteins act as specialized intermediaries that recognize and facilitate the export of target oligosaccharides while excluding precursors, thereby resolving the contradiction between productivity and manufacturing precision.
Solution Approach 2:
The patent modifies the transport parameters by engineering specific membrane transporter proteins with altered substrate specificity or enhanced affinity for complex HMOs. By changing the kinetic parameters of the export system (through protein engineering or overexpression), the process achieves selective export of desired products over precursors, simultaneously improving productivity and manufacturing precision.
2Adaptability or versatility
If the size of the produced oligosaccharide increases, then more complex HMO structures can be synthesized, but the problem of unwanted export of oligosaccharide precursors from the producing cell occurs, leading to an undesirable mix of product and precursor oligosaccharides in the fermentation medium
Solution Approach 1:
The patent applies local quality by introducing exporter proteins with specific substrate recognition capabilities tailored to complex HMO structures. These localized export systems at the cell membrane exhibit selective permeability properties that are optimized for larger oligosaccharides, allowing complex HMOs to be exported while preventing the efflux of smaller precursor molecules, thus maintaining medium purity despite increased structural complexity.
Solution Approach 2:
Instead of trying to prevent precursor export through general membrane impermeability, the patent inverts the approach by introducing specialized exporter proteins that actively facilitate the export of complex HMOs in the opposite direction (from inside to outside the cell). This selective export mechanism indirectly achieves precursor retention by prioritizing the efflux of larger oligosaccharides through specific transport pathways.
3Ease of operation
If multiple transporter proteins are used to transfer mono- or disaccharides across the membrane, then basic sugar transport is achieved, but hardly any knowledge exists on the transport of larger oligosaccharides (e.g., trisaccharides and larger oligosaccharides)
Solution Approach 1:
The patent achieves universality by engineering membrane transporter proteins with broad substrate ranges that can accommodate both small sugars and large oligosaccharides. The engineered transporters (such as modified MFS proteins or SetA variants) possess flexible binding sites and adaptable transport mechanisms that allow them to function across a spectrum of oligosaccharide sizes, thereby providing both ease of operation and versatility for large oligosaccharide transport.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables the production of complex HMOs like lacto-N-triose II and lacto-N-tetraose in large quantities by improving export efficiency and purity, allowing for their recovery from the culture broth.
Implementation Method 1
modifying the expression or activity of a sugar export protein, such that the export of a oligosaccharide into the medium is increased
Data Source
AI summary
The present invention relates to methods for the production of oligosaccharides in genetically modified bacterial host cells, as well as to the genetically modified host cells used in the methods. The genetically modified host cell comprises at least one recombinant glycosyltransferase, and at least one nucleic acid sequence coding for a protein enabling the export of the oligosaccharide.